[Test] Reduce stack usage in async_taskgroup_discarding_neverConsumingTasks.swift.

With optimizations disabled, the InlineArray initializer uses 512kB of stack space. This can overflow the stack depending on exactly how things are set up. Reduce stack usage by manually allocating memory for the array and initializing it as a pointer to Int.

rdar://152420308

Author: mikeash

test/Concurrency/Runtime/async_taskgroup_discarding_neverConsumingTasks.swift

@@ -92,7 +92,15 @@ func test_discardingTaskGroup_bigReturn() async {
   let array = await withDiscardingTaskGroup { group in
     group.addTask {}
     try? await Task.sleep(until: .now + .milliseconds(100), clock: .continuous)
-    return InlineArray<32768, Int>(repeating: 12345)
+
+    // InlineArray.init(repeating:) uses a lot of stack space with optimizations
+    // disabled, so set one up in a less friendly but less stack-consuming way.
+    let ptr = UnsafeMutablePointer<InlineArray<32768, Int>>.allocate(capacity: 1)
+    ptr.withMemoryRebound(to: Int.self, capacity: 32768) {
+      $0.initialize(repeating: 12345, count: 32768)
+    }
+    // Deliberately leak `ptr` to avoid needing to save any temporaries.
+    return ptr.pointee
   }
 
   // CHECK: Huge return value produced: 12345 12345